Method for operating a hydraulic apparatus of a transmission device

ABSTRACT

A method for operating a hydraulic device ( 1 ) of a transmission device having a variable displacement pump ( 2 ) that can be supplied with a hydraulic pressure (p_B) in order to vary the output in the area of an adjusting device ( 3 ), and having at least two pressure circuits (PK, SK) that can be connected to a discharge side ( 24 ) of the adjustable displacement pump ( 2 ) and are assigned different priorities with regard to the supply of hydraulic fluid by the pump. When a change is needed to the operating state of the transmission device for the implementation of which the output of the variable displacement pump ( 2 ) must be elevated relative to its current output, a pressure (p_B) applied in the region of the adjusting device ( 3 ) by a pressure return ( 5 ) is correspondingly modified before changing the operating state.

This application claims priority from German patent application serial no. 10 2010 039 350.9 filed Aug. 16, 2010.

FIELD OF THE INVENTION

The invention relates to a method for operating a hydraulic apparatus of a transmission device.

BACKGROUND OF THE INVENTION

A hydraulic system of a transmission for a vehicle having a variable displacement pump designed with a variable output is known from DE 10 2004 008 611 A1; a pilot pressure can be applied to the adjustment device of the pump in order to vary the output, and the pump can generate a changeable flow of hydraulic fluid for the appropriate supply of different consumers of the transmission. Furthermore, the hydraulic system is designed with at least two pressure circuits arranged on the discharge side of the variable displacement pump that are prioritized differently regarding the supply of hydraulic fluid by the pump. Hydraulic fluid is applied directly by the variable displacement pump to a primary pressure circuit with higher priority. In order to limit the pressure of the primary pressure circuit, a pressure control valve that is able to connect the secondary pressure circuit is provided between the discharge side of the variable displacement pump and a lower-priority secondary pressure circuit. In order to control the output of the variable displacement pump as a function of the operating status, a pressure return is configured between the discharge side of the variable displacement pump and the adjusting device of the variable displacement pump.

If a change in the operating status in the transmission device is required because a greater volume of hydraulic fluid is needed in the transmission device than is currently being provided by the variable displacement pump in the area of the primary pressure circuit and/or the secondary pressure circuit, the pressure decreases in the primary pressure circuit and/or the secondary pressure circuit, and the variable displacement pump is adjusted to provide greater output by the overall force component impinging on the region of the adjusting device.

Disadvantageously, however, the adjustment of the output of the variable displacement pump does not occur until during the change of the operating condition; therefore, the transmission device cannot be operated with the desired spontaneity.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide a method for operating a hydraulic device of the transmission by means of which a transmission device may be actuated with the desired degree of spontaneity.

During the method according to the invention for operating a hydraulic device of a transmission having a variable displacement pump that can be supplied with a hydraulic pressure to vary the output in the area of an adjusting device, and having at least two pressure circuits that may be connected to the discharge side of the variable adjustment pump and that are assigned different priorities regarding the supply of hydraulic fluid by the pump, with a pressure control valve being provided between a higher-priority pressure circuit and a lower-priority pressure circuit that is able to connect the lower-priority pressure circuit for the purpose of limiting the pressure of the higher-priority pressure circuit, with a pressure return being provided downstream of the discharge side of the variable displacement pump in the direction of the adjustment device of the variable displacement pump in order to adjust the output of the variable displacement pump as a function of the operating status, if a change in the operating status of the transmission is needed that requires increasing the output of the variable displacement pump relative to the current output, the pressure applied in the region of the adjusting device by the pressure return is correspondingly modified before the change to the operating status.

When the operating state needs to change in the transmission device, the output of the variable displacement pump is increased to a specific level using the method according to the invention before changing to the operating state characterized by a need for a greater volume of hydraulic fluid, whereby the transmission device is supplied during the entire change of the operating state with the volume of hydraulic fluid necessary to change the operating state without delay, and the transmission device can be operated with the desired high level of spontaneity.

The features indicated in the claims as well as the features indicated in the following exemplary embodiments of the subject matter of the invention are suitable for developing the subject matter of the invention by themselves or in any combination with each other. The combination of a given set of features does not represent a restriction on the development of the subject matter of the invention and is only essentially representative in nature.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional advantages and advantageous embodiments of the subject matter of the invention can be found in the claims and subsequent exemplary embodiments, the principle of which is described with reference to the drawing; for the sake of clarity, the same reference characters are used for components with the same design and function in the description of the different embodiments.

They show:

FIG. 1A highly schematic circuit diagram of a first embodiment of a hydraulic device having three pressure circuits with different priorities and a pressure return that is operated according to the invention;

FIG. 2 A representation of a second embodiment of a hydraulic device corresponding to FIG. 1;

FIG. 3 A circuit diagram of another exemplary embodiment of a hydraulic device in which a valve unit of an adjusting device of a variable displacement pump is designed as a control valve;

FIG. 4 A representation of another embodiment of a hydraulic device corresponding to FIG. 3;

FIG. 5 Another hydraulic device that can be operated according to the invention; and

FIG. 6 Another embodiment of a hydraulic device that can be actuated according to the invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a circuit diagram of a hydraulic device 1 of a transmission device (not shown) for a vehicle. The hydraulic device 1 comprises a variable displacement pump 2 that is designed with a variable output and that can be supplied with a hydraulic pressure p_B in order to vary the output in the region of an adjusting device 3. Two pressure circuits PK and SK are arranged on the discharge side of the variable displacement pump 2 that have different priorities with regard to the supply of hydraulic fluid by the pump. In order to limit the pressure p_PK of the primary pressure circuit PK, a pressure control valve 4 is provided between the higher-priority pressure circuit PK—or the primary pressure circuit—and the lower-priority pressure circuit SK—or the secondary pressure circuit that can connect the lower-priority secondary pressure circuit SK or in the region of which the primary pressure circuit PK may be connected to the secondary pressure circuit SK. In the region of an interface S1, consumers are supplied with pressure p_PK from the primary pressure circuit PK and actuated depending on the operating status.

In order to adjust the output of the variable displacement pump 2 as needed, a pressure return 5 is provided downstream of the discharge side of the variable displacement pump 2 that branches toward the adjusting device 3 of the variable displacement pump 2 in the area of the pressure control valve 4. Furthermore, a valve 6 is provided downstream of the pressure control valve 4, in the region of which a flow q_KS of a third pressure circuit TK, or cooling and lubricating fluid circuit may be adjusted.

The variable displacement pump 2 is designed in the present case as a vane pump whose adjusting ring 7 can be supplied in the region of an effective area 26 with the pressure p_B that is applied via the pressure return 5 and resisted by a spring device 8 acting on another effective area 26. Depending on the current application, the variable displacement pump 2 can also have another suitable pump design with an adjustable displacement volume.

The spring force of the spring device 8 is applied to the adjusting ring 7 of the variable displacement pump 2 such that the variable displacement pump 2 is pivoted toward high outputs when the hydraulic pressure p_B of the pressure return 5 is low, with the variable displacement pump 2 or its output being increasingly reduced against the spring force of the spring device 8 when the values of the hydraulic pressure p_B are high.

Upstream of the variable displacement pump 2, a line L1 branches from the pressure return 5 toward a valve device 9 of the adjusting device 3, the pressure return 5 being connected, via the line L1, to a low-pressure area 12 via a first aperture 10 or a second aperture 11 depending on a switch position of the valve device 9, the low-pressure area being upstream of the fluid pan for the transmission device. The valve device 9 designed as a switching valve 9 in the embodiment of the hydraulic device 1 according to FIG. 1 is supplied in the region of an effective area 13 with a pilot pressure p_VS15 by a pressure adjuster 15 against a spring device 14, with the line L1 in the switching device of the valve device 9 shown in FIG. 1 being connected, via the first aperture 10, to the low-pressure area 12.

If the valve device 9 or its valve spool 27 is moved proceeding by the pilot pressure p_VS15 of the pressure adjuster 15 from its first switching position into its shifted second switching position against the spring device 14, the line L1 is connected, via the second aperture 11, to the low-pressure area 12. The aperture diameter of the first aperture 10 is greater in the present case than the aperture diameter of the second aperture 11, whereby a larger leakage flow flows out of the pressure return 5 through line L1 toward the low-pressure area 12 when the first aperture 10 is open than is the case when the second aperture 11 is opened on the valve device side.

In order to operate a transmission device designed with the hydraulic device 1 according to FIG. 1 at a high level of efficiency over the entire operating range and simultaneously make the variable displacement pump 2 available with a highly dynamic output adjustment, the valve device 9 is moved into its second switching position in which the line L1 is connected, via the smaller aperture, or second aperture 11, to the low-pressure area 12 when the transmission device or a vehicle drivetrain designed with the transmission device is in static mode, during which a lower flow of hydraulic fluid is provided by the hydraulic device 1.

During a dynamic change of the operating state during which a high flow volume of hydraulic fluid is provided via the hydraulic device 1 or its variable displacement pump 2 within a short time, the valve device 9 is moved into the switching position shown in FIG. 1, and the line L1 is connected, via the first, larger aperture 10, to the low-pressure area 12. Then a higher flow volume of leakage fluid flows, via line L1, toward the low-pressure area 12, and the pressure p_B applied in the area of the adjusting device 3 or at the adjusting ring 7 decreases, at a higher gradient than if the second aperture 11 were open, to a level at which the variable displacement pump 2 is pivoted by the spring device 8 in the direction of higher outputs against the pressure p_B.

With a relatively simple design, a dynamic adjustment of the flow of the variable displacement pump 2 is thus achieved as a function of the operating state, and a minimum output of the variable displacement pump 2 is achieved during static operation that only marginally restricts the efficiency of a transmission device, and the transmission device can be operated with an overall high degree of efficiency.

The hydraulic device 1 fundamentally maximizes potential economy since only a very small leakage flow arises the area of the pressure return 5 when a transmission device is in static mode, i.e., in particular when the output shaft is at a constant rotational speed, when the main pressure p_PK in the primary pressure circuit PK is substantially constant, when the transmission device is in a mode where it is not shifted, or during an operating state of the vehicle drivetrain in which basically no actions occur in the transmission device that generate a strong need for a high volume of hydraulic fluid. Consequently, when the necessary primary and secondary pressure levels are reached, the variable displacement pump 2 switches to the position in which the output flow is reduced.

The pump input power is optimally reduced by minimizing the demand in the area of the secondary pressure circuit SK of the hydraulic device 1 in addition to the demand for leakage fluid originating from the pressure return 5 toward the low-pressure area 12. This is the case, for example, when the amount of cooling and lubricating fluid required in the third pressure circuit TK is minimal at low transmission loads.

In order to limit the hydraulic pressure p_B applied to the adjusting device 3 via the pressure return 5 to a maximum above which the functioning of the variable displacement pump 2 would be irreversibly damaged under certain circumstances, a pressure control valve 16 is provided upstream from the variable displacement pump 2 or the adjusting ring 7, the pressure limiting valve being designed in the present case as a check valve and opening upon a preset pressure threshold, with the pressure return 5 being connected to the low-pressure area 12 in a unrestricted fashion in this region when the pressure-control valve 16 is open.

Both the pressure control valve 4 and the valve 6 designed as a combination of a pressure control valve and pressure-reducing valve can be fed a pilot pressure p_VS15 in the manner shown in FIG. 1, the pilot pressure being adjustable in the area of the pressure adjuster 15, with the pressure p_PK in the primary pressure circuit PK and the pressure p_SK of the secondary pressure circuit SK being adjustable depending on the pilot pressure p_VS15. If the hydraulic fluid flow q_KS in the third pressure circuit TK is adjusted independently of the pilot pressure p_VS15 of the pressure adjuster 15, a separate pressure adjuster 17 is assigned to the valve 6 and fed the pilot pressure p_VS17 that is adjustable there, with the connection between the valve 6 and the pressure adjuster 15 then being disconnected.

In addition to switching the valve device 9, the output of the variable displacement pump 2 can also be varied in the hydraulic system 1 according to FIG. 1 by correspondingly changing the flow of lubricant and cooling fluid q_KS in the third pressure circuit TK; for example, if a change in operating state is needed in the transmission device that requires a greater amount of hydraulic fluid to be provided by the hydraulic device 1 or the variable displacement pump 2, the pilot pressure p_VS15 or p_VS17 is elevated and the flow of coolant and lubricating fluid q_KS is increased. Consequently, more hydraulic fluid is guided from the secondary circuit SK via the valve 6 toward the third pressure circuit TK, and less hydraulic fluid is fed into the pressure return, and the pressure p_B decreases. The variable displacement pump 2 then pivots toward a higher output.

The pilot pressure p_VS15 or p_VS17 is elevated at a time at which the increased hydraulic fluid flow demand does not yet exist in the transmission device, although such demand is highly probable given the need for changing the operating state.

Alternately or additionally, in other versions of the above-described procedure for increasing the output of the variable displacement pump 2 in the exemplary embodiments of the hydraulic device 1 shown in the drawing depending on its present use, a hydraulic fluid consumer is activated in one of the pressure circuits PK, SK, and/or TK and/or a leakage fluid flow is activated in one of the pressure circuits, or simultaneously in a plurality of pressure circuits PK, SK and/or TK, preferably by supplying a consumer, such as a pressure adjuster with leakage, with hydraulic fluid, by elevating a flow of cooling fluid of a startup clutch or a double clutch system or the like, which reduces the flow of hydraulic fluid in the pressure return 5 as well as the pressure p_B.

Once the change of the operating state is instigated in the transmission device, the previous need for a greater volume of hydraulic fluid is reduced, for example, by deactivating the consumer that was additionally activated beforehand and/or by reducing the previously increased leakage flow, whereby the elevated delivery rate in the region of the variable displacement pump 2 is fully available for immediately implementing the change in operating state characterized by a need for a greater volume of hydraulic fluid, such as a gear shift during which a hydraulically actuatable shift element within a flow of force in the transmission device is connected by being fed pressure coming from the primary pressure circuit PK.

A second embodiment corresponding to FIG. 1 is shown in FIG. 2, the second embodiment of the hydraulic device 1 essentially corresponding to the first embodiment shown in FIG. 1. For this reason, only the differences between the two embodiments in FIG. 1 and FIG. 2 will be discussed in the following description; with regard to the additional functionality of the hydraulic device 1 in FIG. 2, reference is made to the description of FIG. 1.

The hydraulic device 1 according to FIG. 2 is designed without the pressure control valve 16 in the area of the pressure return 5. Furthermore, the valve device 9 of the adjusting device 3 is moved from the switching position shown in FIG. 2 into its shifted switching position not by the pressure adjuster 15 but by means of another pilot pressure p_VS18 adjustable in the area of another pressure adjuster 18 to connect to the pressure return 5 to the low-pressure area 12 either via the first aperture 10 or the second aperture 11.

In the third embodiment of the hydraulic device 1 shown in FIG. 3, the valve device 9 of the adjusting device 3 is designed as a control valve that can be supplied with the pressure p_B which, in the area of a first effective area 19 of a valve spool 27 of the valve device 9, is applied by the pressure return 5 and is resisted by a spring device 20. Downstream of the first effective area 19 of the valve spool 27 of the valve device 9 is a throttle device 21 in the region of which the pressure p_B is reduced by a specific factor, the pressure p_B21 that is throttled in relation to pressure p_B being applied to a second effective surface 22 of the valve spool 27 of the valve device against which the spring device 20 also impinges. Furthermore, the low-pressure area 12 is provided downstream of the throttle device 21, whereby the hydraulic fluid guided through the throttle device 21 is discharged in the direction of the low-pressure area 12 as a flow of leakage fluid.

The valve device 9 designed with seven control edges 91 to 97 is coupled to the intake side 23 of the variable displacement pump 2 in the region of the fourth control edge 94, and to the discharge side 24 of the variable displacement pump 2 in the region of the control edges 92 and 96. The effective surface 25 of the adjusting ring 7 of the variable displacement pump 2 against which the spring device 8 also impinges can be supplied with pressure via the fifth control edge 95 of the valve device 9, whereas in the area of the other effective surface 26 of the adjusting ring 7 a pressure counteracting the spring device 8 can be applied to the adjusting ring 7 of the variable displacement pump 2 via the third control edge 93 of the valve device 9.

Depending on the overall force component that is applied to the valve spool 27 of the valve device 9 and is adjusted depending on the actuating pressure p_B applied to the first effective surface 19, the throttled pressure p_B21 applied to the second effective surface 22, and the spring force of the spring device 20, the third control edge 93 is either connected to the second control edge 92 or the fourth control edge 94, and the fifth control edge 95 is connected to the sixth control edge 96 or fourth control edge 94. This means that, depending on the position of the valve spool 27, the effective surface 25 of the adjusting ring 7 is either supplied with the pressure from the intake side 23 or the pressure from the discharge side 24 of the variable displacement pump 2, whereas the pressure from the discharge side 24 or pressure from the intake side 23 is applied to the effective surface 26 of the adjusting ring 7.

In contrast to the two embodiments of the hydraulic device 1 shown in FIG. 1 and FIG. 2, the hydraulic pressure p_B applied via the pressure return 5 is not directly used to adjust the output of the variable displacement pump 2. The hydraulic fluid flowing through the pressure return 5 represents a control flow for the valve device 9, thus making it easy to reduce to a minimum the volume flow of hydraulic fluid flowing through the pressure return 5. The overall adjusting force that must be applied to the adjusting ring 7 against the spring device 8 in order to adjust the variable displacement pump 2 is taken directly from the discharge side 24 of the variable displacement pump 2 or is set by the pressure applied there, thus enabling the variable displacement pump 2 to operate with a low power loss and high dynamic adjustment.

In the third embodiment of the hydraulic device 1 shown in FIG. 3, the pressure return 5 branches off of another pressure control valve 28 that is located downstream of the pressure valve 4 and in the region of which the pressure p_SK of the secondary pressure circuit SK is adjusted. As the pressure p_SK of the secondary circuit SK rises, the leakage flow of fluid decreases in the area of the pressure return 5, and the output of the variable displacement pump 2 increases.

The pressure p_SK of the secondary pressure circuit SK is thus lowered in the above-described manner when there is a need to change the operating state in the transmission device for which an increase is anticipated in the volume of hydraulic fluid required from the amount currently provided by the variable displacement pump 2, by correspondingly actuating an additional valve unit 29 downstream of the additional pressure control valve 28 originating from a pressure adjuster 30 assigned to the valve unit 29 with pilot pressure p_VS30, and by means of the associated increase in the lubrication and coolant flow q_KS in the third pressure circuit TK, whereby the variable displacement pump 2 is adjusted toward higher displacement volumes due to the reduced pressure p_B in the pressure return 5 and corresponding actuation of the valve device 9.

FIG. 4 shows a representation of a fourth embodiment of the hydraulic device 1 corresponding to FIG. 3 that only partially differs from the embodiment of the hydraulic device 1 shown in FIG. 3 so that essentially only the differences between the hydraulic device 1 in FIG. 4 and the hydraulic device 1 in FIG. 3 will be discussed in the following description; in regard to the additional functions, reference is made to the description of FIG. 3.

The hydraulic device 1 according to FIG. 4 is designed without the additional pressure control valve 28 of the hydraulic device 1 according to FIG. 3, and the valve device 9 is supplied in the area of the second effective surface 22 with the pilot pressure p_VS15 of the pressure adjuster 15, by means of which the pressure control valve 4 is also controlled in order to connect the pressure chamber 25 of the variable displacement pump 2 to the intake side 23 or the discharge side 24 of the variable displacement pump 2, whereas the other pressure chamber 26 is operatively connected to the discharge side 24 or the intake side 23 of the variable displacement pump 2. As the hydraulic pressure p_B in the pressure return 5 decreases, the output of the variable displacement pump 2 increases.

In the exemplary embodiment of the hydraulic device 1 shown in FIG. 4, the variable displacement pump 2 itself rather than the pump pressure in the region of the discharge side 24 is used to control the pressure in the secondary pressure circuit SK. In contrast to the embodiment of the hydraulic device 1 according to FIG. 3, an additional pressure control valve is not necessary, and the adjusting power for the variable displacement pump 2 is in turn taken directly from the discharge side 24 which is therefore available to a large degree.

In comparison to the hydraulic device 1 according to FIG. 3, the hydraulic device 1 according to FIG. 4 can be operated in the region of the pressure return 5 without a leakage fluid volume flow toward the low-pressure area 12, which allows a transmission device designed with the hydraulic device 1 to be operated over the entire operating range with much greater efficiency in comparison to the hydraulic device 1 according to FIG. 3.

In the embodiments of the hydraulic device 1 according to FIG. 3 and FIG. 4, the maximum pressure difference can be applied to the variable displacement pump 2 or its adjusting ring 7 in the region of the hydraulic device 1, namely between the intake pressure of the variable displacement pump 2 and the pressure side of the variable displacement pump 2. The variable displacement pump 2 can hence be adjusted with maximum dynamics.

FIG. 5 and FIG. 6 show two other embodiments of the hydraulic device 1 that are designed without the valve device 9 in the region of the adjusting device 3, the design of the hydraulic device 1 according to FIG. 5 otherwise corresponding to the design of the hydraulic device 1 according to FIG. 3, and the hydraulic device according to FIG. 6 having the same components as the hydraulic device 1 according to FIG. 1.

The pressure p_B applied via the pressure return 5 in the hydraulic devices 1 according to FIG. 5 and FIG. 6 is guided in each case to the effective surface 26 of the adjusting ring 7 of the variable displacement pump 2, the pressure return 5 upstream of the effective surface 26 being connected, via a throttle device 31, to the low-pressure area 12.

When a change to the operating state in the transmission device is needed that can only be accomplished to the desired degree with a hydraulic fluid requirement that is elevated in comparison to the hydraulic fluid flow for the current output of the variable displacement pump, the pressure p_B applied to the adjusting ring 7 via the pressure return 5 is suitably reduced before the operating state changes in the manner described in FIG. 1 to FIG. 4, for example, by elevating the coolant and lubricating fluid flow q_KS, or by elevating a leakage in the primary pressure circuit PK or in the secondary pressure circuit SK, and the variable displacement pump 2 is adjusted in the direction of higher outputs so that the transmission device can be operated with the desired degree of spontaneity.

REFERENCE CHARACTERS

-   1 Hydraulic device -   2 Variable displacement pump -   3 Adjusting device -   4 Pressure control valve -   5 Pressure return -   6 Valve -   7 Adjusting ring of the variable displacement pump -   8 Spring device -   9 Valve device of the adjusting device -   10 First aperture -   11 Second aperture -   12 Low-pressure area -   13 Effective surface -   14 Spring device -   15 Pressure adjuster -   16 Pressure control valve -   17 Pressure adjuster -   18 Pressure adjuster -   19 Effective surface -   20 Spring device -   21 Throttle device -   22 Second effective surface -   23 Intake side of the variable displacement pump -   24 Discharge side of the variable displacement pump -   25, 26 Effective surface of the adjusting ring of the variable     displacement pump -   27 Valve spool of the valve device -   28 Additional pressure control valve -   29 Valve unit -   30 Pressure adjuster -   31 Throttle device -   91 to 97 Control edge -   L1 Line -   q_KS Coolant and lubricating fluid -   PK Primary pressure circuit -   p_B Hydraulic pressure -   p_B21 Throttled hydraulic pressure -   p_PK Pressure -   p_SK Pressure -   p_VS Pilot pressure -   q_KS Hydraulic fluid volume flow -   S1 Interface -   SK Secondary pressure circuit -   TK Third pressure circuit 

1-11. (canceled)
 12. A method of operating a hydraulic device (1) of a transmission device, the hydraulic device comprising a variable displacement pump (2) that is supplied with a hydraulic pressure (p_B) for varying output in an area of an adjusting device (3), at least two pressure circuits (PK, SK, TK) being connectable to a discharge side (24) of the variable displacement pump (2) are assigned different priorities regarding a supply of hydraulic fluid by the variable displacement pump, a pressure control valve (4) connecting a lower-priority pressure circuit (SK) being provided between a higher-priority pressure circuit (PK) and the lower-priority pressure circuit (SK) for limiting a pressure (p_PK) of the higher priority pressure circuit (PK), and a pressure return (5) being provided downstream of the discharge side (24) of the variable displacement pump (2) in a direction of the adjusting device (3) of the variable displacement pump (2) for adjusting the output of the variable displacement pump (2) as a function of an operating status of the transmission, the method comprising the step of: correspondingly modifying the hydraulic pressure (p_B) applied in the area of the adjusting device (3), when a change in the operating status of the transmission device is necessary whose implementation requires that the output of the variable displacement pump (2) be increased relative to its current output, by the pressure return (5) before the operating status of the transmission changes.
 13. The method according to claim 12, further comprising the step of adjusting the hydraulic pressure (p_B) in the pressure return (5) to a predefined level by elevating a hydraulic fluid flow requirement of at least one consumer suppliable with hydraulic fluid through the higher-priority pressure circuit (PK), and lowering a volume of hydraulic fluid required by the consumer while the operating state of the transmission device is changing.
 14. The method according to claim 12, further comprising the step of adapting the hydraulic pressure (p_B) in the pressure return (5) by varying a hydraulic fluid flow requirement of at least one consumer suppliable with hydraulic fluid through the lower-priority pressure circuit when a change in the operating state of the transmission device is needed, and an elevated displacement volume results in the variable displacement pump (2).
 15. The method according to claim 12, further comprising the step of changing the hydraulic pressure (p_B) in the pressure return (5) depending on a pilot pressure (p_VS15) that can be applied to the pressure control valve (4) when a change in the operating state of the transmission device is needed, and an elevated displacement volume results in the variable displacement pump (2).
 16. The method according to claim 12, further comprising the step of providing, downstream of the pressure control valve (4), another pressure control valve (28) in an area of which a pressure (p_SK) in the lower-priority pressure circuit (SK) and the hydraulic pressure (p_B) in the pressure return (5) is adjusted depending on a pilot pressure (p_VS15) when the change in the operating state of the transmission device is needed, and an elevated displacement volume results in the variable displacement pump (2).
 17. The method according to claim 12, further comprising the step of providing a valve (6) downstream of the pressure control valve (4) in a region of which a hydraulic volume flow (q_KS) of a pressure circuit (TK) located downstream of the lower-priority pressure circuit (SK) is adjustable depending upon a pilot pressure (p_VS15), with the hydraulic pressure (p_B) in the pressure return (5) being adjusted in turn depending on the hydraulic flow volume in the region of the downstream pressure circuit (TK).
 18. The method according to claim 12, further comprising the step of branching the pressure return (5) from the lower-priority pressure circuit (SK), and adjusting the delivery rate of the variable displacement pump (2) by changing the hydraulic fluid flow in the region of the lower-priority pressure circuit (SK).
 19. The method according to claim 12, further comprising the step of supplying a valve device (9) of the adjusting device (3) in a region of an effective surface (19) with a pressure (p_B21) that is throttled relative to the hydraulic pressure (p_B) in the pressure return (5).
 20. The method according to claim 19, further comprising the step of applying a pilot pressure (p_VS18) that is adjustable in a region of a pressure adjuster (18) in area of a second effective surface (22) of the valve device (9).
 21. The method according to claim 12, further comprising the step of supplying at least one of a cooling and a lubricating fluid circuit (TK) with hydraulic fluid via the lower-priority pressure circuit (SK).
 22. The method according to claim 12, further comprising the step of supplying at least one of a cooling and a lubricating fluid circuit with hydraulic fluid via a pressure circuit (TK) located downstream of the lower-priority pressure circuit (SK).
 23. A method of operating a hydraulic device (1) of a transmission device as a function of an operating state of the transmission device, the hydraulic device (1) comprising a variable displacement pump (2) and an adjustment device (3), the adjustment device (3) being supplied with a hydraulic pressure (p_B) and adjusting an output of the variable displacement pump (2) as a function of the hydraulic pressure (p_B), at least a priority pressure circuit (PK) and a secondary pressure circuit (SK) being connectable to the output (24) of the variable adjustment pump (2), the priority pressure circuit (PK) having a higher priority of being supplied with hydraulic fluid from the variable adjustment pump (2) than the secondary pressure circuit (SK), the priority pressure circuit (PK) being directly coupled to the output of the variable displacement pump (2), a pressure control valve (4) being connected between the priority pressure circuit (PK) and the secondary pressure circuit (SK) for limiting pressure (p_PK) of the priority circuit (PK), a pressure return (5) being located downstream of the output (24) of the variable displacement pump (2) and directing the hydraulic pressure (p_B) to the adjustment device (3), the hydraulic pressure (p_B) being adjustable along the pressure return (5) for adjusting the output of the variable displacement pump (2) as a function of the operating state of the transmission device, the method comprising the steps of: adjusting the hydraulic pressure (p_B), before changing the operating state of the transmission device, when the output of the variable displacement pump (2) needs to be increased relative to a current output of the variable displacement pump (2) in order to implement the change in the operating status of the transmission device. 